Hi & Welcome to the forums!
I assume you are using Logic 8.0.2?
Is your friend using the same version?
Do you use the same plug-ins?
What version of OS X are you using?
What is the exact error message?
The .logic file is damaged or Files Missing?
Are you receiving only the .logic file or the whole project folder with sub folders?
Here are my tips:
1. When saving your Logic project, make sure you tick save assets (e.g. audio files and samples specific to YOUR system)
2. Save the logic project.
3. Go to a Finder window and find the project folder.
4. Inside should be your .logic project file, an Audio Files folder, a Project file backups folder, and Undo Data folder and perhaps a Bounces folder and Samples folder etc, too.
5. Copy the main folder to a USB stick, burn to CD or DVD or compress the folder and send via the internet.
(To compress the folder: Ctrl-click on the folder and select "Compress *****"
Hope that helps?